Heat pumps with evohome

[sandyman]

I wasn't sure that I knew the answer to your question, because the heat pump installers never discussed this with me. However, I have had a closer look. The cable from the BDR91 goes into the back of the Panasonic heat pump controller and a separate wire comes out of the heat pump controller to the secondary pump. This implies I am using the "optional heat pump controller connection". However, on checking the Honeywell controller I can see the BDR91 is not set for hear pump controls, hence it looks more likely the evohome is only controlling the secondary pump. In order to answer your question fully I will need to get back to my heat pump installer, or perhaps I might just have a play and see what I can find.

I wonder if the panasonic heat pump controller is doing all the hard work, and the evohome BDR just being an external "call for heat" . See if you can see from the panasonic controller manual what the input that the BDR 91 is wired to does - if its labelled "3rd party thermostat" or something like that?
Ian

[spiralp]

I wonder if the panasonic heat pump controller is doing all the hard work, and the evohome BDR just being an external "call for heat" . See if you can see from the panasonic controller manual what the input that the BDR 91 is wired to does - if its labelled "3rd party thermostat" or something like that?
Ian

I think you are correct. From what I can see I have the earlier BDR91, which only allows for basic switching, rather than the later version which allows some heat pump control. I have looked through the documentation I have, but I do not have anything showing how the controller is wired. In fact, I think the documentation I have does not include everything that should have been provided. This is probably because my heat pump installation was completed just as we entered the first lockdown in March 2020, so the 'hand over' was done by phone. My relationship with the installer is good so I will go through all the documentation with them in March next year when the heat pump is next serviced.

[sandyman]

I think you are correct. From what I can see I have the earlier BDR91, which only allows for basic switching, rather than the later version which allows some heat pump control. I have looked through the documentation I have, but I do not have anything showing how the controller is wired.

if it was me, I'd download the manuals, take the cover off and follow the cables, buts its your system so your choice (btw I'm not suggesting that you change anything)

I think given that you have a control system that is still treating the heat pump as an on/off boiler, you'll be getting a TPI input to the heatpump control - which may not be ideal for what the heatpump expects. Given that you have a good relationship with your installer, I'd be really interested to hear what they think . I don't know what the difference in behaviour is if you use the new BDR that has the "heatpump" binding options.

[sidepipe]

I'll absolutely be an outlier here but I'm using Evohome with a combination of a gas boiler and air source heat pumps ( Daikin ) in several rooms. No direct link... just using BDR91s as dummy actuators plus room stats and using Domoticz for IP control of the heat pumps, tracking the EvoHome set point for the rooms in question.

[spiralp]

An update to my earlier experience of using Evohome with a Panasonic heat pump. My installer has decided the two products are not compatible and has completely disengaged all Evohome control of the heat pump. All my Evohome now does is control the TRVs. The heat pump decides as and when to produce heat and at what temperature based on a weather compensation curve. This has eliminated cycling and significantly improved my heat pump efficiency. I am now of the opinion that heat pumps are best controlled by radiator sizing, radiator balancing and flow temperature (weather compensated).

[sandyman]

An update to my earlier experience of using Evohome with a Panasonic heat pump. My installer has decided the two products are not compatible and has completely disengaged all Evohome control of the heat pump. All my Evohome now does is control the TRVs. The heat pump decides as and when to produce heat and at what temperature based on a weather compensation curve. This has eliminated cycling and significantly improved my heat pump efficiency. I am now of the opinion that heat pumps are best controlled by radiator sizing, radiator balancing and flow temperature (weather compensated).

that maybe makes sense for the flow temperature contorl but - how does the heatpump know that it needs to come on in the first place? there must be something?

[spiralp]

The heat pump has its own controls. There is a simple on/off for heating at whatever external temperature I set. Mine is set at 18deg, below which temperature the heat pump is ready to provide heat. The heat pump also has a weather compensation curve, which sets the heating flow temperature depending on external temperature, mine is set to 48deg at -5deg reducing to 32deg at +15deg. The heat pump heats a 30 litre buffer tank and monitors the deltaT of the flow to the buffer tank, only providing heat when necessary. Hence if the external temperature is, say, 16 deg the heat pump is ready to operate. However, if the house is quite warm (such that the deltaT is below 5deg) then no heat is provided. The heating circulation pump is controlled by both pressure and by the heat pump. Most of my Evohome TRVs are now set to wide open, but with balancing via the lockshield valves, and provide the correct room temperature as a result of the weather compensated flow temperature. A few of my Evohome TRVs are used as limiters to avoid some rooms getting too hot (e.g. on days when there is significant solar gain). To put it simply, the heat pump is on all the time. There is a timer function, but I do not use this.